This invention relates to a contact lens and, more particularly, to a contact lens having, above all, an excellent oxygen permeability.
Contact lenses now in extensive use may be classified into an oxygen-permeable hard contact lens, referred to hereinafter as a GP contact lens, and a water-containing soft contact lens. The water-containing soft contact lenses, which may be worn more comfortably, are unsatisfactory in oxygen permeability of the lens material. While it may be contemplated to raise the water content of the lens material to thereby raise its oxygen permeability, such lens may be contaminated easily by bacteria, according to recent clinical reports, to cause serious complications to cornea or conjunctiva. The GP contact lenses, on the other hand, have been highly evaluated because of high oxygen permeability, astigmatism curative effects, durability and safety, and have come to be used predominantly as the contact lenses. In keeping therewith, studies and investigations of the GP hard contact lenses are progressing briskly. However, special emphasis is put only on the oxygen permeability of the conventional GP contact lenses with disregard to other properties required of the contact lenses.
For example, the contact lenses described in Japanese Laid-open Patent Applications Nos. 8769/1987, 61928/1987 and 36646/1988 are excellent in oxygen permeability, but are unsatisfactory in shape stability or resistance to contamination. On the other hand, the contact lenses disclosed in Japanese Laid-open Patent Application Nos. 99720/1987 and 212618/1987 are formed of dialkyl fumarate, which is poor in copolymerizability and, even when it is copolymerized ultimately, it is so brittle that it can be cracked easily, causing danger to users. The contact lens disclosed in Japanese Laid-open Patent Application No. 176909/1986 is low in oxygen permeability and unsuitable for continuous wearing in the eye, to which special attention has been directed recently.